For central banks, fantasy monetary policy would mean handing out money directly to the population

When modern banking first emerged in medieval Italy, European mathematicians regarded negative numbers as absurd. Six hundred years on, the successors to the Medicis and Peruzzis face negative interest rates—and while negative numbers are now widely accepted, negative rates are not.

Negative rates invert the norms of banking. Borrowers are paid for taking money, while savers pay to hand over a deposit. High-level opposition from savers should be little surprise; this month has seen high-level opposition from two of their...

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Central banks across the globe are trying a radical approach to boost economic growth: negative interest rates. But what are negative rates and will they work? Image: Adele Morgan/The Wall Street Journal